Liver is an important biological system that plays a key role in regulating energy supply of the body. This organ maintains a program of glucose release and storage in response to hormonal stimulation establishing glucose homeostasis. The disruption of energy metabolism by toxicants has serious pathophysiological consequences and is connected to diabetes and obesity. Traditional approaches for measuring cellular metabolism require large cell numbers, reveal little about metabolism dynamics, do not allow exposure of cells to multiple stimuli in parallel and do not permit to study the interplay between multiple cell-types cultured together. Thus, the traditional cell culture / metabolite detection approaches are not suited for monitoring scarce cells (e.g. primary human hepatocytes) and screening the effects of drug candidates and toxicants on the liver cells. The goal of this proposal is to develop a novel lab-on-chip biosensor platform for in vitro monitoring of liver cell metabolism. The novelty of the proposed platform is based on our ability to integrate micro-biosensors for multiple metabolites with functional microfabricated liver cell cultures. The juxtaposing of cells and sensing elements will be achieved by fabricating poly(ethylene glycol) (PEG) hydrogel microstructures serving dual function as cell culture chambers and matrices for enzyme encapsulation. Enzyme-containing PEG hydrogel microchambers will be built on top of cell culture substrates, creating individually addressable cell culture units for electrochemical detection of glucose and fluorescence-based detection of hydrogen peroxide (H2O2). The proposed biosensor platform will offer several advantages including monitoring two analytes simultaneously, observing dynamic and reciprocal metabolic interactions of two distinct cell phenotypes, and utilizing small numbers of cells for analyses. A microfluidic delivery system will be incorporated with the sensing module to control composition of the soluble environment. A novel microfabricated device integrating functional liver cells with miniature biosensors will be an important enabling technology in the study of the effects of hepatotoxicants on liver function. PUBLIC HEALTH RELEVANCE Liver is the metabolic center of human body and is largely responsible for detoxification and energy regulation functions. Energy regulation refers to the program of consumption and production of sugars such as glucose. Imbalance in energy regulation is closely connected diabetes and obesity. We propose to build a microchip for monitoring sugar consumption in liver cells. This microchip will be used to determine how harmful substances affect the liver and its ability to regulate sugar levels in the body.